1. Technical Field
Embodiments of the present invention relate to a device for compensating ripples in the output voltage of a PFC (power factor correction) converter and a battery charging device for an electric vehicle that uses such compensating device, which can reduce the ripple voltage in the output voltage of the PFC converter without using a high-capacitance electrolyte capacitor.
2. Description of the Related Art
A device for charging the battery of an electric vehicle (EV) generally uses commercial power. Thus, the battery charging device for an electric vehicle can be used for 110 Vac or 220 Vac and may require consideration of power factor correction. In order to allow charging for batteries of various specifications, the battery charging device for an electric vehicle may be required to provide a wide range of output, such as from 100 V to 500 V.
For this purpose, an electric vehicle battery charging device 100 is generally used that has a dual composition as illustrated in FIG. 1, including an AC/DC converter 110 for power factor correction (PFC), and a high-voltage link capacitor 120 for converting the varying power of AC voltage to a more stable DC power and a DC/DC converter 130 that uses a transformer for charge control.
FIG. 2 is a diagram illustrating the form of power within the conventional battery charging device 100 for an electric vehicle shown in FIG. 1.
Referring to FIG. 2, a conventional charging device 100 for an electric vehicle may rectify an AC input and may perform current control at the power factor correction terminal such that the current at the input side follows the rectified voltage, and in such cases, a PFC converter 400 such as that illustrated in FIG. 3 may be used. In such a case, fluctuating power may occur at the output end of the PFC converter 400, and a high-voltage DC link capacitor may be used for filtering. Then, the DC/DC converter, which uses a transformer for insulation, may charge the battery via current control by using the DC voltage formed at the AC/DC terminal.
However, the conventional electric vehicle charging device 100 described above has a complicated structure, due to its dual composition. Also, the conventional electric vehicle charging device 100 may require an electrolytic capacitor having a high capacitance of several thousand uF or higher and a high power density for filtering the fluctuating power, but since the lifespan of an electrolytic capacitor decreases rapidly at high temperatures, it is not suitable for applications requiring long lifespans, such as electric vehicles.
A method of using a film capacitor instead of an electrolyte capacitor can be considered as a solution, but a film capacitor has a much lower power density compared to an electrolyte capacitor and thus may not be suitable for a charger that is designed for high capacitance and requires high power density.